Adult: Tarsal setae aa I present (Fig. 10) (correlates with character in phoretic deutonymphs). External vertical setae (ve) situated on the same transverse line with internal vertical setae (vi), long and barbed (Fig. 10). Genu I with solenidion σ' no more than three times longer than σ'' (Fig. 10). Scapular setae si longer than setae se (Fig. 10). All hysterosomal setae except c1 elongate, longer than the distance to the next posterior seta (Fig 11).

Species identification

Keys to species are not available for this genus. This genus needs a revision. Reliable identification is possible after examining type specimens and DNA sequencing. Taxonomic problems are centered around the European species Kuzinia laevis versus two North American species: Kuzinia affinis and Kuzinia americana. The two latter species have been cited to have a distinctly different number of foliate setae on tarsi I-IV (Delfinado and Baker, 1976). However, our examination of North American specimens (i.e., ex Bombus vagans, Rhode Island) indicate that the morphology of tarsal setae is essentially the same between North American and European specimens. In addition, character states separating Kuzinia affinis and Kuzinia americana (e.g., body length, shape, and length of sternum) may represent allometric effects and/or differences in the pressure applied to specimens during slide preparation. The same problem is apparent in a recent study that reported four species of Kuzinia (including the European species, Kuzinia laevis) associated with two species of bumble bees from Argentina (Revainera et al., 2014).

Distribution

Nearctic, Palaearctic, Neotropical, and Oriental regions. Introduced to the Australian region (Australia, Tasmania, and New Zealand) with commercial bumble bee colonies used for crop pollination.

Bee hosts

primarily associated with bumble bees (Bombus), but can occasionally be found on other bees

Host association level

Permanent

associated exclusively with bees or their close relative, wasps; cannot live without these hosts

Temporary

some life stages are associated with bees, while others are not

Facultative or opportunistic

can complete entire life cycle without bees or their close relative, wasps

permanent

Host associations, feeding, and dispersal

All stages live in nests of bumble bees, where they feed on pollen, nematodes, and fungi.

Mite phoretic deutonymphs disperse and overwinter on adult queen bees. Phoresy on workers and males of bumble bees or cuckoo bumble bees has also been documented.

Biology

Occasionally, phoretic deutonymphs of Kuzinia can be found on other bees, wasps, other insects, and in rodent burrows (which can be nesting sites for bumble bees). One little-known species described in Kuzinia, Kuzinia sciurina, was reported from a squirrel nest, a non-bee association. "Kuzinia" recki, reported in forest litter, does not belong to Kuzinia.

In nests of bumble bees, Kuzinialaevis mites feed on pollen, honey, bumble bee cocoon material, nest organic debris (Chmielewski, 1969), nematodes, and fungi (R. W. Husband pers. comm. in Grobov, 1978), without any noticeable harmful effect on their hosts or at the boundary of being a harmless commensal and a pest (Chmielewski, 1969). Large numbers of mites, however, may be of concern for bumble bee colonies introduced for commercial pollination; these bees usually have low genetic variation and hence low disease resistance (Allen et al., 2007). In literature Kuzinialaevis has also been indicated as a potential pest of pollen harvested from honey bees by humans (Chmielewski, 1991b).